1. Field of the Invention
The present invention relates to a magnetic disk memory device and, more particularly, to a magnetic disk memory device having the functions of removing dust from the internal air thereof and cooling the same.
2. Description of the Prior Art
In a magnetic disk memory device in which a magnetic disk is used as the recording medium, magnetic recording and reproduction is effected by a magnetic head which is floated by the balance of aerodynamical forces to form a slight gap of an order of serveral .mu.m between itself and the surface of the magnetic disk. This system is considered to be more reliable than the conventional system in which the magnetic head is held always in contact with the magnetic disk, because the wear of the magnetic head and magnetic disk is suppressed. For this reason, the "floating system" in which the magnetic head floats above the surface of the magnetic disk has become popular.
In adopting this floating system, it is required to diminish as much as possible the dust suspended by the air in the space between the magnetic head and the magnetic disk, in order to preserve a highly stable floating gap between the magnetic disk and the magnetic head. The elimination of the dust is essential to avoid a phenomenon called "head crush" in which the magnetic disk and/or the magnetic head is damaged by dust particles of several .mu.m coming into the gap between the magnetic head and the magnetic disk which moves at a speed of several tens of meters per minute.
Generally, the magnetic disk memory device is equipped with an air filter for filtrating the internal air to remove the dust. More specifically, an air filter capable of removing dust particles of particle sizes exceeding 0.3 .mu.m at a high rate of 99.97 to 99.99% is disposed at a suitable portion of the air passage to filtrate the air before the latter is supplied to the region around the magnetic disk and magnetic head of the memory device.
Hitherto, the following air filtration systems (a) to (c) have been proposed.
(a) An external air take-in system in which external fresh air is continuously taken into the device. The air is filtrated by a filter and, after flowing in the conduit, is discharged to the outside. This external air supply system is disclosed in U.S. Pat. No. 3,710,540.
(b) An internal air circulation system in which a closed loop for circulation of air is formed in the magnetic disk memory device to include an air filter. Air is circulated by the flow induced as a result of rotation of the magnetic disk. This system is shown in U.S. Pat. No. 3,710,540.
(c) An external air supplementary system in which, in order to prevent the induction of external air due to a vacuum established in the space defined by a shroud which houses the magnetic disk, a blower is disposed at a suitable portion in the air passage to pressurize the air from the outside. An example of this system is shown in U.S. Pat. No. 4,008,492. These air filtration systems, however, suffer the following disadvantages (A), (B) and (C).